Within the scope of minimally-invasive surgery, such as endoscopic or laparoscopic surgery, access to the operating site is made via small incisions in the body of the patient (such as the abdomen or thorax), in which the practitioner places a canula formed by a tube whereof the diameter varies from 3 to 15 mm, via which the practitioner can insert into the body of the patient either an endoscope for obtaining a video image on a monitor, or long and fine instruments for performing a procedure at the operating site.
The majority of existing instruments is constituted by a fine (typically around 5 mm in diameter) and rigid elongated body (typically around 30 cm long). The proximal end of the instrument comprises a grip handle for the practitioner and the distal end of the instrument is often fitted with a forceps or scissors, optionally capable of transmitting electric current for cutting (monopolar or bipolar).
The main advantage of laparoscopic surgery is the minimum incisions. However, the main limitation is the decrease in dexterity associated with a remote access by long instruments. Indeed, when the instrument is rigid, its passage via a fixed incision point is a planar kinematic constraint which limits the number of degrees of freedom (DoF) to four: three movements of rotation about the point of incision and a penetration translation movement of the instrument. In particular, with conventional laparoscopic rigid instruments, it is impossible to bend the distal end of the instrument to orient the forceps optimally relative to the practitioner. This is a major application limitation of laparoscopic surgical tools for surgical procedures.
This has led to the development of novel instruments comprising a distal part exhibiting mobility relative to the principal body of the instrument. For example, for suturing exercise, the surgeon utilises a curved needle. When he carries out this exercise in optimal conditions, the surgeon:                1. grasps the needle such that the plane of the needle is perpendicular to the axis of the forceps;        2. places the plane of the needle perpendicularly to the edges to be sutured;        3. turns the needle according to an axis perpendicular to its plane to insert into the tissue to be sutured,Therefore, to make a suture in favourable conditions, there must be provision for placing the axis of the instrument substantially parallel to the edges to be sutured and turning the forceps about its axis. During some interventions, positioning the points of incision relative to the operating site is such that it is not possible to align the axis of the forceps with the edges to be sutured when using rigid instruments, substantially complicating making the suture. This is why instruments have been developed which orient the axis of the forceps relative to the principal axis of insertion of the instrument in the body, due to distal mobility.        
It should be noted that the final rotation movement of the forceps on itself (intrinsic rotation of the forceps), which controls penetration of the needle, must be made with a high precision and a maximal stability of the direction of the axis of the forceps while applying sufficient force to perforate tissue.
Instruments having a distal mobility are described in documents U.S. Pat. No. 7,338,513, U.S. Pat. No. 7,316,681, U.S. Pat. No. 7,398,707 and US 20080228196.
The instruments described in these documents are such that the axis of the forceps can be oriented relative to the principal axis of insertion of the instrument according to rotation made about any axis perpendicular to the principal axis of insertion. This is done either by a system with flexible sleeve and cables (document U.S. Pat. No. 7,338,513) or by using two perpendicular pivot joints (document U.S. Pat. No. 7,398,707). In both cases, two rotational degrees of freedom between the principal axis of insertion and the axis of the forceps result from the mechanism used. By using the intrinsic rotation of the axis of insertion, freed by the canula placed at the level of the point of insertion, it is therefore possible to combine three rotations and produce all preferred orientations of the forceps. However, to produce the movement described previously for a suturing exercise, that is, intrinsic rotation of the forceps, in general a complex combination of these three movements and their synchronisation is required at the level of their actuation, making carrying out the exercise very complex. With a design having sleeves and cables (document U.S. Pat. No. 7,338,513), the rigidity of the assembly is insufficient and the axis of the forceps can remain stable and turn on itself when forces are exerted, only with difficulty. With a system having pivots and three combined rotations, a complex robotic system is required to perform synchronisation of movements (document U.S. Pat. No. 7,398,707).
Other documents describe instruments for which movement of the forceps occurs without resulting from a combination of three rotations. In the document U.S. Pat. No. 7,241,288, the forceps is operated by a system of gears and can be either bent (orientation of the axis of the forceps), or oriented about its axis (intrinsic rotation). However, for controlling one or the other of the movements, a mechanical clutch must be used. The movements are therefore not controlled directly by independent proximal movements.
The instruments described in the document U.S. Pat. No. 6,913,613 comprise a flexible rod, though rigid to torsion according to its axis, enabling orienting a distal forceps according to its axis and a rigid control rod of the inclination of this forceps relative to an axis of the tool. The two rods extend in a tube. The instrument is difficult to make and is complex.
An aim of the invention is to provide a surgical instrument being simple in use, and which addresses at least one of the limitations and drawbacks mentioned above.